Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants, which can include particulate matter (PM) and/or soot, hydrocarbons, and gaseous compounds including, inter alia, the oxides of nitrogen (NOX) included therein. Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of pollutants exhausted including, inter alia, NOX emitted to the atmosphere by an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
In order to comply with the regulation of NOX, some engine manufacturers have implemented a strategy called selective catalytic reduction (SCR). SCR is a process where a reductant, most commonly urea ((NH2)2CO) or a water/urea solution, is selectively injected into the exhaust gas stream of an engine and absorbed onto a downstream substrate. The injected urea solution decomposes into ammonia (NH3), which reacts with NOX in the exhaust gas to form water (H2O) and diatomic nitrogen (N2). However, numerous complexities and trade-offs may be present in the implementation of various strategies to control emissions, including, inter alia, those which can be presented by interrelationships between NOX conversion efficiency, package sizing, cost, system backpressure, and fuel efficiency.
U.S. Patent Publication No. 2011/0079003 A1 (the '003 publication) to Sun et al., filed as U.S. patent application Ser. No. 12/573,469 on Oct. 5, 2009, discloses an aftertreatment system which includes an SCR catalyst and a reductant system. The reductant system includes an injector or nozzle that introduces a reductant into an exhaust flow which is introduced to the SCR catalyst via an exhaust pipe. The exhaust pipe includes a straight part and a curved part or bend upstream from the straight part, and the nozzle is mounted in the bend. The length of the straight part of the exhaust pipe or distance between the nozzle and SCR catalyst may be sufficiently long to achieve the mixing of reductant into the exhaust flow and provide adequate dwell time for the urea reductant to convert into NH3. In one embodiment, the straight part of the pipe includes a mixer. An indentation is provided in an outer curve of the upstream bend and additionally provides a recessed area or pocket for the nozzle to be located. The indentation may help prevent the formation of the deposits, which may cause higher backpressure and disrupt the flow and mixing of urea reductant into the exhaust flow, by directing the droplets or spray from the nozzle down the straight part of the exhaust pipe.
The present disclosure is directed to mitigating or eliminating one or more of the drawbacks discussed above.